Intake system for internal combustion engines having at least two carburettors



Apnl 29, 1969 G. NELSON 3,441,008

INTAKE SYSTEM FOR INTERNAL COMBUSTION ENGINES HAVING AT LEAST TWO CARBURETTORS Filed on. 50. 19s? United States Patent US. Cl. 12352 6 Claims ABSTRACT OF THE DISCLOSURE In an intake system for internal combustion engines having at least two carburettors which are connected by individual ducts to separate cylinders, each duct is provided with a shut-off valve which at idling speed and low engine output is closed and causes the fuel-air mixtures from the carburettors to fiow into a common mixing chamber before entering the cylinders. As the throttle valves are gradually opened the shut-off valves are also opened so that at high engine output the mixtures pass substantially directly into the cylinders.

This invention relates to an intake system for internal combustion engines having at least two carburettors.

The maximum output of an internal combustion engine is determined i.a. by the volumetric efiiciencies of the cylinders. In a multicylinder engine having a single carburettor it is therefore diflicult to maintain a high volumetric efiiciency at high output, and besides the volumetric efficiencies are likely to be dilferent in different cylinders. In order to eliminate this inconvenience, the intake system may be provided with a plurality of carburettors each of which feeds few cylinders, such as two cylinders, provided that the individual carburettors in all operating positions supply equal amounts of fuel-air mixture of similar composition. Since it has proved difficult in practice to effect equal adjustments of the carburettors and, consequently, smoother running of the engine especially at idling speed and low output, attempts have been made to solve the problem by providing a connecting pipe between the individual intake pipes of the engine such that the mixture from one carburettor to a certain degree can affect the mixture from another carburettor. However, the result thereof is not entirely satisfactory because the comparatively low vacuum at low speeds does not render possible suflicient equalization and because variations in the supply from the individual carburettors are likely to occur.

The object of this invention is to provide an intake system for a multi-carburettor engine which ensures smooth running throughout the whole range of speed and in spite thereof maintains the advantage of highest possible volumetric efficiency at high output and facilitates adjustment of the carburettors resulting in a lower fuel consumption.

An embodiment of the invention will be described with reference to the annexed drawing in which:

FIG. 1 is a diagrammatic sectional view of the intake system of a four-cylinder engine having two carburettors, and

FIG. 2 is a detail view of the operating means for two valves provided in the proximity of each carburettor.

Referring to FIG. 1, the intake system comprises two carburettors 1 and 2 which are associated with throttle valves 4 and 5, respectively, adapted to be synchronously turned by a connecting rod 3. The throttles may be 0p- 3,441,008 Patented Apr. 29, 1969 erated by an accelerator pedal, not shown. Each carburettor is connected in the usual manner to an individual main duct 6 and 7, respectively, which in turn is divided into branch ducts 8, 9 and 10, 11, respectively, communicating with their respective cylinders of the engine 30. Each main duct 6, 7 communicates with a side duct 12 and 13, respectively, said side ducts leading to a common mixing chamber 14. Return ducts 15 and 16 extend from the mixing chamber to the respective main ducts 6 and 7 and open therein at a place ahead of the branch ducts. Inserted in each main duct 6 and 7 is a hinged shut-off valve 17 and 18, respectively, inserted between the respective side ducts 12, 13 and the outlet of the respective return duct 15, 16. All of the valves 4, 5 and 17, 18 are spring-biased to closed position.

One wall of the mixing chamber 14 forms part of the wall of an exhaust pipe 19 of the engine so that heat can be easily transmitted to the mixing chamber 14 and to the fuel-air mixture flowing therethrough, in order to facilitate atomization of the mixture. The advantage of this arrangement is that the combustion in the engine will be as complete as possible and that the contents of unburnt fuel in the exhaust gases will be low, but at the same time the volumetric efficiency will be lower than without preheating, resulting in a slightly reduced engine power. Inserted in the mixing chamber 14 are members, such as flanges 20, which project into the flow paths and cause turbulence of the gas flow and thereby also contribute to the atomization and vapourization of the fuel drops so as to obtain a homogeneous mixture.

The mode of operation of the system is as follows.

When the engine is idling and under low load the valves 17 and 18 are closed and the fuel-air mixtures from the carburettors 1 and 2 pass beyond the throttles -4 and 5, respectively, and through the side ducts 12 and 13, respectively, into the mixing chamber 14 where they are mixed and heated and subjected to turbulence whereupon they are passed to their respective main duct through the return ducts 15 and 16, respectively. Control of the supply to the engine is effected exclusively by the two synchronously adjustable throttle valves 4 and 5. The individual carburettors need not be extremely accurately adjusted, provided that the composition of the common mixture obtained in the chamber 14 is correct.

After the throttles 4 and 5 have been opened to such an extent, preferably to an angle of between 30 and 40, that the full flow capacity of the side ducts 12, 13 is obtained, the shut-off valves 17 and 18 are successively opened corresponding to full output while the throtles 4 and 5 are opened still more until free passages are obtained for the flow of fuel-air mixture from the carburettors 1 and 2 directly into the main ducts 6 and 7. The main part of the mixture flows directly into the cylinders without perceptible preheating resulting in a high volumetric efficiency and maximum output of the engine. Even then a minor flow of fuel-air mixture will pass through the side ducts, mixing chamber and return ducts resulting in an equalization of differences in the adjustments of the carburettors and in the elimination of overheating of the mixing chamber.

Adjustment of the valves 17, 18 and the valves 4, 5 should of course be effected by a common control. FIG. 2 illustrates an embodiment in which the opening angle of the throttles 4 and 5 directly controls adjustment of the valves 17 and 18. Since the arrangement is the same for both carburettors, it will be described with reference only to the throttle 4.

The angularly adjustable throttle 4 is mounted on a spindle 21 secured to a lever 22 which by means of a linkage of wire 28 is connected for instance to an accelerator pedal. The lever 22 has a projection 24 formed with a cam 23. While in FIG. 2 the cam 23 is straight it may be curved and have a constant or varying radius of curvature. The position of the projection 24 shown in full lines corresponds to the closed position of the throttle. The shut-off valve 17 is angularly adjustable about a spindle 25 which carries a second lever 26 which at its end has an abutment, such as a roller 27. In FIG. 2 the position of the lever 26 shown in full lines corresponds to the closed position of the valve 17.

To increase the output of the engine at low load the lever 22 and the projection 24 thereof are turned counterclockwise as viewed in FIG. 2 whereas the lever 26 remains in its position shown in which the valve 17 is closed. The lever 26 is acted upon only after the projection 24 has been turned to the position 24a shown in dotted lines in which the cam 23 comes into contact with the abutment or roller 27 Upon continued turning movement of the lever 22 and the projection 24 to the position 24b the lever 26 will be turned to the position shown in dotted lines in which both the throttle 4 and the valve 17 are fully open. Since the roller 27 during turning movement of the lever 26 will roll along the cam 23 at a gradually increasing distance from the spindle of the throttle, the turning angle of the valve 17 will increase more and more relative to the turning angle of the throttle 4, and the valve and the throttle will simultaneously assume their fully open positions.

It will be obvious that the operating means may be devised in a manner different from the above described provided that the movements of the two valves are synchronized such as to obtain the above described mutual movements.

What I claim is:

1. An intake system for a multi-cylinder internal combustion engine having at least two carburettors, comprising individual main ducts connecting the individual carburettors to separate cylinders and having each a throttle and a downstream shut-01f valve, a common mixing chamber for fuel-air mixtures from the carburettors, side ducts leading from each main duct at a place between said throttle and said valve to said mixing chamher, return ducts leading from said mixing chamber back to said main ducts downstream of said valve, and a device for adjusting said valves such that at idling speed and low engine output the valve is closed and the whole mixture is caused to pass through the mixing chamber, whereas at high engine output the valve is opened so as to permit substantially the whole mixture to pass directly from the respective carburettors to the cylinders.

2. An intake system as claimed in claim 1, characterized in that the mixing chamber is formed in connection with an exhaust pipe of the engine such that the exhaust gases from the engine are able to preheat the fuel-air mixture flowing through said chamber.

3. An intake system as claimed in claim 1, characterized in that the mixing chamber comprises means for subjecting the fuel-air mixture to turbulence.

4. An intake system as claimed in claim 3, characterized in that said means consist of flanges projecting into the flow path.

5. An intake system as claimed in claim 1, wherein said device is adapted for operating said throttle in each main duct of the carburettor to control the supplied amount of fuel-air mixture and is also adapted at a certain opening angle of the throttle to act upon, and on increasing opening angles successively to open, said valve in the main duct from closed to fully open position.

6. An intake system as claimed in claim 5, characterized in that said device consists of a lever mounted on the spindle of the throttle and having a projection with a cam face cooperating with a cam follower on a corresponding lever on the spindle of the shut-off valve in the main duct.

References Cited UNITED STATES PATENTS 1,763,726 6/1930 Timian. 1,767,031 6/1930 Worthington l23--122 1,872,800 8/1932 Paton. 2,016,694 10/1935 Timian. 2,323,442 7/ 1943 Beard. 2,761,437 9/1956 Stolte 123-127 3,303,832 2/1967 Platner et al. 3,338,568 8/1967 Mangoletsi.

AL L. SMITH, Primary Examiner.

US. Cl. X.R. 123122, 127 

